Wash kale. Pull greens away from the stalks, discarding stalks. Shred by hand into small pieces.
Heat large wok . Add oil and swirl around. Add onion & leek and stir-fry 3 minutes. Add garlic, bell peppers & carrot. Continue stir-frying until onions are tender and peppers are beginning to soften but still crisp.
Add the broccoli and pepper flakes, if using.and stir. Add the kale, cover and reduce heat to medium. Simmer for 5 minutes or until kale is tender, but still crisp, not too soft.
Remove lid and let any excess liquid evaporates. Use two forks to mix the bean sprouts through the other ingredients. Add salt & pepper to taste.
Transfer to serving plate and scatter nuts over the top, and serve with lemon wedges.